A polycarbonate resin produced from bisphenol A, etc. has excellent thermal stability and mechanical characteristics, and therefore is used as a material for various parts in an electrical and electronics field, an automotive field, and the like. However, depending on the application, there are occasional demands for flame retardancy and impact resistance which cannot be satisfied by the polycarbonate resin comprising bisphenol A.
On the other hand, a polycarbonate-polydimethylsiloxane copolymer (PC-PDMS copolymer) is known as a polycarbonate resin having excellent flame retardancy and impact resistance (see, for example, PTL 1). The PC-PDMS copolymer can provide a molded product having improved lubricity, abrasion resistance, and the like. As the molded product thereof, there are known, for example, a cast film, an extrusion molded film, and the like (see, for example, PTL 2-5).
Furthermore, the characteristic features exhibited by the PC-PDMS copolymer are exhibited depending on the number of the repeating siloxane units. For example, a PC-PDMS copolymer having n, the number of the repeating siloxane units, ranging from 40 to 60, specifically a PC-PDMS copolymer having n of 49, shows good low temperature impact properties (see, for example, PTL 6); there is known a process for obtaining a transparent PC-PDMS copolymer by using PDMS having n, the number of the repeating siloxane units, of 50 (see, for example, PTL 7); and there is known a PC-PDMS copolymer using PDMS having n, the number of the repeating siloxane units, of 0 to 20, which is transparent and flame retardant (see, for example, PTL 8).
As described above, it is known that the PC-PDMS copolymer, due to the characteristic features thereof, can be developed for many applications including a helmet with a transparent visor (see, for example, PTL 9), a material for manufacturing key top members, and the like.
Further, with regard to the PC-PDMS copolymer, it is known to modify both molecular ends of the raw material PDMS. As a process for producing the modified PDMS, there are known, for example, (1) a process wherein polydimethylsiloxane is reacted with allylphenol and, thereafter, excess allylphenol is removed by washing with aqueous alcohol (see, for example, PTL 1), (2) a process wherein polydimethylsiloxane is reacted with eugenol (2-methoxy-4-allylphenol) and, thereafter, low molecular weight organosiloxane compounds are removed by evaporation (see, for example, PTL 11), and the like.
And recently, a material which possesses the characteristics of the above-mentioned PC-PDMS copolymer has come to be desired in many applications and it became necessary to adapt the material to a variety of shapes of the molded products. Therefore, it is necessary to secure fluidity of the resin and the temperature of the molding process tends to increase.
However, there has been a problem that the PC-PDMS copolymer tends to become yellow more easily than a general polycarbonate resin during a high temperature molding process. There is no information available on this yellowing unique to the PC-PDMS copolymer and improvement thereof.